Experimental analgesic nephropathy

To What is the Alternative?

Summary

The value of conventional long-term, carcinogenicity or reproductive studies would in many instances appear to depend upon the “insurance” they are held to provide and upon “no effect” levels, rather than upon the production of adverse effects that can be extrapolated to man. The development of alternatives to such studies necessitates refinement of the latter and the investigation of specific components and mechanisms of toxicity.

Direct toxicity of nonsteroidal antiinflammatory drugs for renal medullary cells

Antipyretic analgesics, taken in large doses over a prolonged period, cause a specific form of kidney disease, characterized by papillary necrosis and interstitial scarring. Epidemiological evidence incriminated mixtures of drugs including aspirin (ASA), phenacetin, and caffeine. The mechanism of toxicity is unclear. We tested the effects of ASA, acetaminophen (APAF, the active metabolite of phenacetin), caffeine, and other related drugs individually and in combination on mouse inner medullary collecting duct cells (mIMCD3). The number of rapidly proliferating cells was reduced by approximately 50% by 0.5 mM ASA, salicylic acid, or APAF. The drugs had less effect on confluent cells, which proliferate slowly. Thus, the slow in vivo turnover of IMCD cells could explain why clinical toxicity requires very high doses of these drugs over a very long period. Caffeine greatly potentiated the effect of acetaminophen, pointing to a potential danger of the mixture. Cyclooxygenase (COX) inhibitors, indomethacin and NS-398, did not reduce cell number except at concentrations greatly in excess of those that inhibit COX. Therefore, COX inhibition alone is not toxic. APAF arrests most cells in late G(1) and S and produces a mixed form of cell death with both oncosis (swollen cells and nuclei) and apoptosis. APAF is known to inhibit the synthesis of DNA and cause chromosomal aberrations due to inhibition of ribonucleotide reductase. Such effects of APAF might account for renal medullary cell death in vivo and development of uroepithelial tumors from surviving cells that have chromosomal aberrations.

Analgesic nephropathy in rodents

While it is clear that humans suffer from "classic" analgesic nephropathy, the causative agents and mechanisms are still not known. A review of the literature revealed that chronic acetaminophen exposure does not produce renal papillary necrosis in rodents or humans. In contrast, while chronic aspirin exposure to rodents results in renal papillary necrosis with renal morphological and functional changes similar to that described in humans, epidemiological studies do not implicate aspirin alone in human analgesic nephropathy. The difference in the effects of aspirin in humans and rats may be due to the inability of epidemiological studies to detect aspirin-induced analgesic nephropathy or more likely to the fact that species differences exist, with the rat being more sensitive than humans. With respect to combinations of aspirin and acetaminophen, with or without caffeine, there are minimal tightly controlled studies. In addition, there is little evidence of enhanced renal papillary necrosis in rodents treated with aspirin and acetaminophen combinations. In summary, it remains to be determined what chemical entities cause "classic" analgesic nephropathy in humans and the mechanisms of this toxicity such that preventative measures can be instituted. Elucidation of the mechanisms of analgesic nephropathy has been hampered due to the lack of animal models that closely mimic the human disease. Rodents do not appear to be an appropriate model.

Acetaminophen: acute and chronic effects on renal function

Acetaminophen (APAP) is normally metabolized in the liver and kidney by P450 enzymes. No toxicity is observed with therapeutic doses of APAP. However, after ingestion of large quantities of APAP (>2,000 mg/kg), highly reactive quinones, metabolites of APAP, are generated; these react with glutathione and sulfhydryl groups on critical proteins, resulting in cellular dysfunction and hepatic and renal toxicity. The P450 metabolizing enzymes differ somewhat in character between the liver and kidney. Factors that enhance renal toxicity include chronic liver disease, possibly gender, concurrent renal insults, and conditions that alter the activity of P450-metabolizing enzyme systems. Acute renal toxicity is characterized by cellular injury primarily confined to the proximal tubule and significant reductions in glomerular filtration rate. However, there is little evidence that chronic administration of APAP contributes to chronic renal disease and analgesic nephropathy. The only report on this subject suggests that combination therapy with aspirin is required for medullary damage in rats. No evidence exists for the development of chronic analgesic nephropathy with APAP alone. Epidemiologic studies in healthy individuals have failed to demonstrate a significant correlation between APAP use and chronic renal disease and classic analgesic nephropathy. Therefore, large doses of APAP can produce both renal and hepatic failure, but little evidence exists for production of classic analgesic nephropathy with the use of APAP alone.

Acetaminophen/aspirin mixtures: experimental data

The pertinent literature concerning the experimental induction of analgesic nephropathy is reviewed. Based on the accumulated data from animal experiments that induced a pathologic lesion resembling chronic analgesic nephropathy, of the limited number of analgesics tested, aspirin seems to be the most nephrotoxic of the commonly available analgesics. When aspirin is combined with other analgesics, the limited data available suggest at least an additive nephrotoxic effect, if not a synergism. The histologic presentation of acute intoxication is substantially different from that following chronic ingestion. With improvements in pathologic analysis of experimental results, future studies may well provide more insight as to the significance, relative contribution, and risk of combination analgesic products in inducing experimental analgesic nephrotoxicity.

Analgesic nephropathy in Fischer 344 rats: comparative effects of chronic treatment with either aspirin or paracetamol

This study has compared the relative nephrotoxicity of chronic treatment with aspirin or paracetamol in an animal model. Changes in renal structure and urinary concentrating ability were examined in female Fischer 344 rats after continuous treatment with either aspirin (120-230 mg/kg body wt/day), or paracetamol (140-210 mg/kg body wt/day), and were compared with age-matched untreated control rats. Renal morphological changes were examined after 40-83 weeks of analgesic treatment, using light and electron microscopy. Aspirin caused renal papillary necrosis and a decrease in urinary concentrating ability, whereas paracetamol alone did not cause significant renal damage. Aspirin produced damage to the interstitial cells and matrix, particularly in the mid-papillary region, followed by changes to the thin limbs of the loop of Henle and medullary capillary endothelium. These structural changes were similar to those described previously, when continuous treatment with combined aspirin and paracetamol was studied in the same animal model.

Crystalluria, medullary matrix crystal deposits and bladder calculi associated with an acutely induced renal papillary necrosis

A single (100 mg/kg) intraperitoneal dose of 2-bromoethanamine hydrobromide induced renal papillary necrosis (RPN) acutely in rodents and caused a transient crystalluria between 4 and 8 h after dosing. These crystals comprised struvite or magnesium ammonium phosphate (MAP) as assessed by shape, solubility, infra-red spectrum and X-ray microprobe analysis. Acid-soluble, bi-refringent crystals were also present within the renal medullary matrix during the same time period as the crystalluria. The presence of the MAP was associated with loss of the anionic renal medullary mucopolysaccharides staining. A total of 5/64 rats with a 2-bromoethanamine-induced renal papillary necrosis and monitored for up to 160 days had bladder calculi that were predominantly MAP. These data suggest that medullary mucopolysaccharide matrix disruption associated with RPN leads to a release of previously bound cations, super-saturation and the nucleation of crystalline MAP. These processes could also be implicated in the formation of MAP bladder calculi.

High resolution light microscopic morphological and microvascular changes in an acutely induced renal papillary necrosis

Morphological changes were followed in semi-thin glycolmethacrylate sections, after treating male Wistar rats with a single ip dose of 2-bromoethanamine (BEA) hydrobromide (100 mg/kg) to induce renal papillary necrosis. Medullary interstitial cells had irregular nuclei at 4 hr and focal necrosis by 8 hr which spread from the papilla tip to the cortico-medullary junction from 12 hr. Increased mucopolysaccharide staining was observed in the papilla tip at 4 hr, and was lost from those regions where necrosis had developed by 48 hr. Endothelial platelet adhesion, first seen at 8 hr, was very marked at 18 hr, but affected capillaries in necrotic regions only, up to 144 hr. The absence of extravasated Monastral Blue B demonstrated the integrity of the medullary microvascular endothelia. The distal nephron showed degenerative changes at 12 hr and cell exfoliation at 18 hr. Cortical changes were confined to PAS-positive casts in the collecting duct and loop of Henle from 8 hr and dilatation of distal and proximal tubules at 8 and 72 hr, respectively. There was active repair at the junction between viable and necrotic tissue in the papilla from 24 hr with mitoses in the collecting ducts and loops of Henle. Normally the urothelium is less than 3-4 cells thick, but upper urothelial proliferation followed BEA administration. Hyperplasia was especially marked at the mouth of the ureter and in the pelvis opposite the region of necrosis (7-8 cells thick at 18 hr) and had only partially resolved by 144 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 1

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 2

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Cadmium, analgesics, and the chronic progressive nephrosis in the female Sprague-Dawley rat

Female Sprague-Dawley rats received phenacetin or aspirin at average daily doses of 135 and 27 mg/kg respectively in the diet and either demineralized water (DMW) or a 100 ppm cadmium (Cd) solution as their drinking water for 12 months. This dose of Cd produced borderline tubular toxicity, as measured by the excretion of IV-injected human beta 2-microglobulin. The kidney accumulation of Cd just reached the critical level of 200 ppm in all groups at the end of the study. The various treatments did not significantly affect growth, creatinine clearance, urine osmolality and the urinary excretion of beta-N-acetyl-D-glucosaminidase and aminoacids. No interaction resulted from the concomitant administration of analgesics and Cd. Both aspirin subgroups (receiving DMW or Cd) showed an attenuation of the age-related decline of the renal function as revealed by a lower urinary excretion of albumin and total protein. The accentuation of the mesangial matrix seen upon aging was also partly inhibited in the aspirin rats.

The role of metabolic activation of analgesics and non-steroidal anti-inflammatory drugs in the development of renal papillary necrosis and upper urothelial carcinoma

There has been no cogent hypothesis to explain the molecular basis of analgesic and non-steroidal anti-inflammatory drug (NSAID) associated renal papillary necrosis (RPN) and upper urothelial carcinoma (UUC). The microsomal cytochrome P-450 enzyme system may generate reactive intermediates which promote pathophysiological effects in the lung, liver and renal cortex, but the absence of P-450 activity in the medulla suggests that it is unlikely that similar events lead to RPN and UUC. Other enzymes (eg. peroxidases) convert substituted aromatics into benzoquinoneimines (an intermediate that has previously been defined in P-450-mediated toxicity). The medulla is rich in fatty acid peroxidases involved in the metabolism of arachidonic acid. NSAID and analgesics interact with key enzymes in this pathway, which could lead to the co-oxygenation of exogenous and endogenous compounds via the peroxidase, lipoxygenase, or prostaglandin hydroperoxidase enzymes. The generation of reactive molecules in the medulla could explain both RPN and UUC via the alkylation of macromolecules. The formation of free radicals would give rise to extensive lipid peroxidation, (there are large quantities of free polyunsaturated fatty acids in the medullary interstitial cells), an event of major potential importance to local cell destruction and genotoxic effects. At present this proposed mechanism of co-oxygenation offers the most attractive working hypothesis to explain the molecular pathogenesis of both RPN and UUC.

Changes in medullary glycosaminoglycan histochemistry and microvascular filling during the development of 2-bromoethanamine hydrobromide-induced renal papillary necrosis

A single dose of 2-bromoethanamine (BEA) hydrobromide induced an apex limited renal papillary necrosis (RPN) at low doses (50 mg/kg, ip and sc, or 100 mg/kg, po), and the total ablation of the medulla at high doses (greater than 150 mg/kg, ip and sc, or 1000 mg/kg, po) in both male and female Wistar rats. BEA (at levels of 50, 100, and 150 mg/kg ip to male rats) caused transient hydropic changes. By 12 to 24 hr the anatomical elements of the medulla were necrosed, and active regeneration and reepithelialization of the viable areas was apparent. The only cortical changes up to 120 hr were dilatation of the nephron and the Bowman's spaces. The medullary glycosaminoglycan matrix (assessed by histochemical staining with colloidal iron) gave an intense granular appearance 2 hr after BEA, which was more marked and diffuse in the apex of the medulla from 8 to 12 hr. The staining was lost from those areas where early necrotic changes had occurred by 12 to 24 hr, and there was no subsequent staining of matrix material up to 120 hr. Vascular filling with colloidal carbon particles suggested an early shift of blood flow to the outer medulla at 2 to 4 hr, followed by the sustained filling of the microvasculature of the medulla well into the period when frank necrotic change was apparent. These data suggest that changes in the medullary matrix might play a previously unrecognized role in the development of 2-bromoethanamine hydrobromide-induced renal papillary necrosis, and these changes may give rise to loss of the material that supports the medullary capillaries.

Renal toxicity of aspirin to rats pre-treated with ethinyl oestradiol

Castrated rats receiving aspirin at a dose level of 1000 mg/kg showed necrosis of the proximal convoluted tubules, similar to that seen in female rats, and the extent of this lesion was increased by oestrogen pre-treatment. Urinary gamma-glutamyl transpeptidase activity was a useful indicator of the necrotic changes induced.

Eighteen month oral study of aspirin, phenacetin and caffeine, in C57Bl/6 mice

Groups of 40 male and 40 female C57BL/6 mice were maintained for 75-80 weeks on meal form diets containing aspirin, phenacetin and caffeine either singly or in combination. The maximum daily doses of phenacetin alone and the APC combination were approximately one-half of their previously determined respective oral LD50's. Mild, nonprogressive histopathologic changes of the urinary tract were noted with these changes first evident in animals given the highest dose of phenacetin. Sulfhemoglobinemia was also induced in all groups of animals given phenacetin alone or in combination indicating that toxic doses were administered oral LD50's. Mild, nonprogressive histopathologic changes of the urinary tract were noted with these changes first evident in animals given the highest dose of phenacetin. Sulfhemoglobinemia was also induced in all groups of animals given phenacetin alone or in combination indicating that toxic doses were administered oral LD50's. Mild, nonprogressive histopathologic changes of the urinary tract were noted with these changes first evident in animals given the highest dose of phenacetin. Sulfhemoglobinemia was also induced in all groups of animals given phenacetin alone or in combination indicating that toxic doses were administered. Under the conditions of this study, evidence of carcinogens was not demonstrated for any of the drugs given alone or in combination.